medium -> large users database crashes bbPress

I already posted a trac ticket, but I am going to post here in the hopes that someone with a larger bbPress site might have an answer for me.

I have a medium sized bbPress forum setup with about 32,000 members and about 400,000 topics. Decent size but not large by any means. I have friends who run vb sites with hundreds of thousands of users and tens of millions of posts, so I am a small fry.

The Problem:
I am getting constant out of memory errors in my database, and many times this will even lead to a 500 error on the front end.

One area I am having a problem with is anywhere dealing with users. For instance, on the wp-admin page there is a box ‘right now in the forums’ which gives details such as # of users posts etc.

Without exception if I have bbPress installed, my page errors out on that box and it is blank. I look in my error log and see the out of memory errors.

The amount of memory that I assign doesn’t seem to matter, I have gone as high as 1GB for the site but still get the error

This is making my entire network of sites completely unstable and almost completely useless. I’d hate to loose bbPress as that is the entire reason I built this in the first place.

Does anyone have ideas on how to solve these issues?

*how to remove the happening now box on wp-admin
*how to clean up or optimize any functions pulling the members list (my user_meta table is almost 800,000 rows)